Ultrasonic signal processor for a hand held ultrasonic diagnostic instrument

ABSTRACT

A hand held ultrasonic instrument is provided in a portable unit which performs both B mode and Doppler imaging. The instrument includes a transducer array mounted in a hand-held enclosure, with an integrated circuit transceiver connected to the elements of the array for the reception of echo signals. A digital signal processing circuit performs both B mode and Doppler signal processing such as filtering, detection and Doppler estimation, as well as advanced functions such as assembly of multiple zone focused scanlines, synthetic aperture formation, depth dependent filtering, speckle reduction, flash suppression, and frame averaging.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation of U.S. application Ser. No.10/151,583 (019162-000132US), filed on May 16, 2002, which was acontinuation of U.S. application Ser. No. 09/630,165 (019162-000131),filed on Aug. 1, 2000, which was a continuation-in-part of U.S.application Ser. No. 09/167,964 (U.S. Pat. No. 6,135,961),(019162-00130), filed on Oct. 6, 1998, which was a continuation-in-partof U.S. application Ser. No. 08/863,937 (U.S. Pat. No. 5,817,024),(019162-000120), filed on May 27, 1997, which was a continuation-in-partof U.S. application Ser. No. 08/826,543 (U.S. Pat. No. 5,893,363),(019162-000110), filed on Apr. 3, 1997, which was a continuation-in-partof U.S. application Ser. No. 08/672,782 (U.S. Pat. No. 5,722,412),(019162-000100), filed on Jun. 28, 1996, the full disclosures of whichare incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] This invention relates to medical ultrasonic diagnostic systemsand, in particular, to a fully integrated hand held ultrasonicdiagnostic instrument.

BRIEF SUMMARY OF THE INVENTION

[0003] As is well known, modern ultrasonic diagnostic systems are large,complex instruments. Today's premium ultrasound systems, while mountedin carts for portability, continue to weigh several hundred pounds. Inthe past, ultrasound systems such as the ADR 4000 ultrasound systemproduced by Advanced Technology Laboratories, Inc., assignee of thepresent invention, were smaller, desktop units about the size of apersonal computer. However, such instruments lacked many of the advancedfeatures of today's premium ultrasound systems such as color Dopplerimaging and three dimensional display capabilities. As ultrasoundsystems have become more sophisticated they have also become bulkier.

[0004] However, with the ever increasing density of digital electronics,it is now possible to foresee a time when ultrasound systems will beable to be miniaturized to a size even smaller than their much earlierancestors. The physician is accustomed to working with a hand heldultrasonic scanhead which is about the size of an electric razor. Itwould be desirable, consistent with the familiar scanhead, to be able tocompact the entire ultrasound system into a scanhead-sized unit. Itwould be further desirable for such an ultrasound instrument to retainas many of the features of today's sophisticated ultrasound systems aspossible, such as speckle reduction, color Doppler and three dimensionalimaging capabilities.

[0005] In accordance with the principles of the present invention, adiagnostic ultrasound instrument is provided which exhibits many of thefeatures of a premium ultrasound system in a hand held unit. Thesepremium system features are afforded by a digital signal processorcapable of performing, both greyscale and Doppler signal processingincluding their associated filtering, compression, flash suppression andmapping functions, as well as advanced features such as syntheticaperture formation, multiple focal zone imaging, frame averaging, depthdependent filtering, and speckle reduction. In a preferred embodimentsthe digital signal processor is formed on a single integrated circuitchip. This sophisticated ultrasound instrument can be manufactured as ahand held unit weighing less than five pounds.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006]FIG. 1 illustrates in block diagram form the architecture of ahand-held ultrasound system of the present invention;

[0007]FIGS. 2a and 2 b are front and side views of a hand-heldultrasound system of the present invention which is packaged as a singleunit;

[0008]FIGS. 3a and 3 b are front and side views of the transducer unitof a two-unit hand-held ultrasound system of the present invention;

[0009]FIG. 4 illustrates the two units of a hand-held ultrasound systemof the present invention in a two-unit package;

[0010]FIG. 5 is a block diagram of the digital signal processing ASIC ofthe ultrasound system of FIG. 1;

[0011]FIG. 6 is a flowchart of B mode processing by the digital signalprocessing ASIC;

[0012]FIG. 7 is a flowchart of Doppler processing by the digital signalprocessing ASIC; and

[0013]FIG. 8 is a chart of the user controls of the ultrasound system ofFIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

[0014] Referring first to FIG. 1, the architecture of a hand-heldultrasound system of the present invention is shown. It is possible topackage an entire ultrasound system in a single hand-held unit onlythrough judicious selection of functions and features and efficient useof integrated circuit and ultrasound technology. A transducer array 10is used for its solid state, electronic control capabilities, variableaperture, image performance and reliability. Either a flat or curvedlinear array can be used. In a preferred embodiment the array is acurved array, which affords a broad sector scanning field. While thepreferred embodiment provides sufficient delay capability to both steerand focus a flat array such as a phased array, the geometric curvatureof the curved array reduces the steering delay requirements on thebeamformer. The elements of the array are connected to atransmit/receive ASIC 20 which drives the transducer elements andreceives echoes received by the elements. The transmit/receive ASIC 20also controls the active transmit and receive apertures of the array 10and the gain of the received echo signals. The transmit/receive ASIC ispreferably located within inches of the transducer elements, preferablyin the same enclosure, and just behind the transducer. A preferredembodiment of the transmit/receive ASIC is described in detail in U.S.Pat. No. 5,893,363 for ULTRASONIC ARRAY TRANSDUCER TRANSCEIVER FOR AHAND HELD ULTRASONIC DIAGNOSTIC INSTRUMENT.

[0015] Echoes received by the transmit/receive ASIC 20 are provided tothe adjacent front end ASIC 30, which beamforms the echoes from theindividual transducer elements into coherent scanline signals. The frontend ASIC 30 also controls the transmit waveform timing, aperture andfocusing of the ultrasound beam through control signals provided for thetransmit receive ASIC. In the illustrated embodiment the front end ASIC30 provides timing signals for the other ASICs and time gain control. Apower and battery management subsystem 80 monitors and controls thepower applied to the transducer array, thereby controlling the acousticenergy which is applied to the patient and minimizing power consumptionof the unit. A memory device 32 is connected to the front end ASIC 30;which stores data used by the beamformer. A preferred embodiment of thefront end ASIC is described in detail in U.S. Pat. No. 5,817,024 forHAND HELD ULTRASONIC DIAGNOSTIC INSTRUMENT WITH DIGITAL BEAMFORMER.

[0016] Beamformed scanline signals are coupled from the front end ASIC30 to the digital signal processing ASIC 40. The digital signalprocessing ASIC 40 filters the scanline signals, processes them as Bmode signals, Doppler signals, or both, and in the preferred embodimentalso provides several advanced features including synthetic apertureformation, frequency compounding, Doppler processing such as powerDoppler (color power angio) processing, and speckle reduction as morefully detailed below. The ultrasound B mode and Doppler information isthen coupled to the adjacent back end ASIC 50 for scan conversion andthe production of video output signals. A memory device 42 is coupled tothe back end ASIC 50 to provide storage used in three dimensional powerDoppler (3D CPA) imaging. The back end ASIC also adds alphanumericinformation to the display such as the time, date, and patientidentification. A graphics processor overlays the ultrasound image withinformation such as depth and focus markers and cursors. Frames ofultrasonic images are stored in a video memory 54 coupled to the backend ASIC 50, enabling them to be recalled and replayed in a liveCineloop® realtime sequence. Video information is available at a videooutput in several formats, including NTSC and PAL television formats andRGB drive signals for an LCD display 6.0 or a video monitor.

[0017] The back end ASIC 50 also includes the central processor for theultrasound system, a RISC (reduced instruction set controller) processor502. The RISC processor is coupled to the front end and digital signalprocessing ASICs to control and synchronize the processing and controlfunctions throughout the hand-held unit. A program memory 52 is coupledto the back end ASIC 50 to store program data which is used by the RISCprocessor to operate and control the unit. The back end ASIC 50 is alsocoupled to a data port configured as an infrared transmitter or a PCMCIAinterface 56. This interface allows other modules and functions to beattached to or communicate with the hand-held ultrasound unit. Theinterface 56 can connect to a modem or communications link to transmitand receive ultrasound information from remote locations. The interfacecan accept other data storage devices to add new functionality to theunit, such as an ultrasound information analysis package.

[0018] The RISC processor is also coupled to the user controls 70 of theunit to accept user inputs to direct and control the operations of thehand-held ultrasound system.

[0019] Power for the hand-held ultrasound system in a preferredembodiment is provided by a rechargeable battery. Battery power isconserved and applied to the components of the unit from the powersubsystem 80. The power subsystem 80 includes a DC converter to convertthe low battery voltage to a higher voltage which is applied to thetransmit/receive ASIC 20 to drive the elements of the transducer array10.

[0020]FIGS. 2a and 2 b illustrate a one piece unit 87 for housing theultrasound system of FIG. 1. The front of the unit is shown in FIG. 2a,including an upper section 83 which includes the LCD display 60. Thelower section 81 includes the user controls as indicated at 86. The usercontrols enable the user to turn the unit on and off, select operatingcharacteristics such as the mode (B mode or Doppler), color Dopplersector or frame rate, and special functions such as three dimensionaldisplay. The user controls also enable entry of time, date, and patientdata. A four way control, shown as a cross, operates as a joystick tomaneuver cursors on the screen or select functions from a user menu.Alternatively a mouse ball or track pad can be used to provide cursorand other controls in multiple directions. Several buttons and switchesof the controls are dedicated for specific functions such as freezing animage and storing and replaying an image sequence from the Cineloopmemory.

[0021] At the bottom of the unit 87 is the aperture 84 of the curvedtransducer array 10. In use, the transducer aperture is held against thepatient to scan the patient and the ultrasound image is displayed on theLCD display 60.

[0022]FIG. 2b is a side view of the unit 87, showing the depth of theunit. The unit is approximately 20.3 cm high, 11.4 cm wide, and 4.5 cmdeep. This unit contains all of the elements of a fully operationalultrasound system with a curved array transducer probe, in a singlepackage weighing less than five pounds. A major portion of this weightis attributable to the battery housed inside the unit.

[0023]FIGS. 3 and 4 illustrate a second packaging configuration in whichthe ultrasound system is housed in two separate sections. A lowersection 81 includes the transducer array, the electronics through to avideo signal output, and the user controls. This lower section is shownin FIG. 3a, with the curved transducer array aperture visible at thebottom. The lower section is shown in the side view of FIG. 3b. Thislower section measures about 11.4 cm high by 9.8 cm wide by 2.5 cm deep.This unit has approximately the same weight as a conventional ultrasoundscanhead. This lower section is connected to an upper section 83 asshown in FIG. 4 by a cable 90. The upper section 83 includes an LCDdisplay 82 and a battery pack 88. The cable 90 couples video signalsfrom the lower unit 81 to the upper unit for display, and provides powerfor the lower unit from the battery pack 88. This two part unit isadvantageous because the user can maneuver the lower unit and thetransducer 84 over the patient in the manner of a conventional scanhead,while holding the upper unit in a convenient stationary position forviewing. By locating the battery pack in the upper unit, the lower unitis lightened and easily maneuverable over the body of the patient.

[0024] Other system packaging configurations will be readily apparent.For instance, the front end ASIC 30, the digital signal processing ASIC40, and the back end ASIC 50 could be located in a common enclosure,with the beamformer of the front end ASIC connectable to different arraytransducers. This would enable different transducers to be used with thedigital beamformer, digital filter, and image processor for differentdiagnostic imaging procedures. A display could be located in the sameenclosure as the three ASICs, or the output of the back end ASIC couldbe connected to a separate display device. Alternatively, the transducerarray 10, transmit/receive ASIC 20 and front end ASIC 30 could be in thetransducer enclosure and the balance of the system in the battery anddisplay unit. The configuration of FIG. 4 could be changed to relocatethe user controls onto the display and battery pack unit, with theultrasound ASICs located in the unit with the transducer array.

[0025] Referring to FIG. 5, a detailed block diagram of the digitalsignal processing ASIC 40 is shown. Scanline signals from the front endASIC 30 are received by a normalization circuit 410, where they aremultiplied by a variable coefficient supplied by coefficient memory 408to normalize the received signals for aperture variation. When thetransducer is receiving signals along the scanline from shallow depths,a relatively small aperture, such as four or eight transducer elements,is used to receive echo signals. As the reception depth along thescanline increases, the aperture is incrementally increased so that thefull 32 element aperture is used at maximum depths. The normalizationcircuit 410 will multiply the received scanline signals by appropriatecoefficients over the range of aperture variation, such as factors offour or eight, to normalize the signals for this aperture variationeffect.

[0026] When the ultrasound system is operated in the B mode to form astructural image of tissue and organs, the digital signal processor isoperated as shown by the flowchart of FIG. 6. The normalized echosignals follow two paths in FIG. 5, one of which is coupled to a fourmultiplier filter 412 and the other of which is coupled by a multiplexer422 to a second four multiplier filter 414. Each multiplier filterincludes a multiplier and an accumulator which operate as an FIR (finiteimpulse response) filter. Scanline echo signals are shifted sequentiallyinto a multiplier, multiplied by coefficients supplied by thecoefficient memory 408, and the products are accumulated in theaccumulator at the output of the multiplier. The coefficients for thefilter 412 are chosen to multiply the echo signals by a cosine functionand the coefficients for the filter 414 are chosen to multiply the echosignals by a sine function, preparatory for I and Q quadrature signaldetection. The four multiplier filters produce accumulated signals at arate which is less than the input rate to the multipliers, therebyperforming decimation band pass filtering. When the signal bandwidthexceeds the display bandwidth of the display monitor, the image lineswill flicker due to an abasing condition. The decimation filtering isdesigned to reduce the signal bandwidth as well as the data rate tomatch the display bandwidth of the monitor. By applying a succession ofinput signals and coefficients to a multiplier and accumulatingintermediate products, the effective length of the filter can beincreased. For instance, input signals 1-8 can be sequentially weightedby the fourth multiplier and the products accumulated in the fourthaccumulator; input signals 3-10 can be weighted by the third multiplierand the products accumulated in the third accumulator; input signals5-12 can be weighted by the second multiplier and the productsaccumulated in the second accumulator; and input signals 7-14 can beweighted by the first multiplier and the products accumulated in thefirst accumulator. The data rate has thereby been decimated by two, andeach multiplier and accumulator is effectively operated as an eight tapfilter. Thus it is seen that the effective number of taps of the filteris a product of the number of multipliers (four in this example) and thedecimation rate (two in this example).

[0027] Additionally, this filter reduces r.f. noise and quantizationnoise through its bandwidth limiting effects. I and Q echo signalsamples are produced at the outputs of filters 412 and 414, amplified ifdesired by the multipliers of gain stages 416 and 418, then stored inthe r.f. memory 420. The Q samples are coupled to the r.f. memory by amultiplexer 426.

[0028] When a synthetic aperture image is to be formed, partially summedscanlines from a portion of the full aperture are acquired followingseparate pulse transmissions, then combined to form full aperturescanlines. When the synthetic aperture is formed from two pulsetransmissions, the I and Q samples from the scanline of the first halfof the aperture are stored in the r.f. memory 420 until the I and Qsamples from the other half of the aperture are received. As the samplesfrom the second half of the aperture are received, they are combinedwith their spatially corresponding counterparts by an adder 424. Thesize of the r.f. memory is kept to a minimum by storing the aperturesignals after decimation filtering, which reduces the size of the memoryrequired to store the scanline signal samples.

[0029] After the I and Q samples for the full aperture have been formed,the echo samples are coupled from the adder 424 to a detection andcompression circuit 428. This circuit includes two shift registers and amultiplier arranged to form a CORDIC processor for performing envelopedetection of the form (I²+Q²)^(1/2). See, for instance, “The CORDICTrigonometric Computing Technique, by J. E. Voider, IRE Trans. on Elect.Computers, (Sep. 30, 1959). The detected signal is compressed and scaledto map the detected signals to a desired range of display gray levels.

[0030] Following detection and compression mapping, the grayscalesignals are lowpass filtered in an FIR filter 432, then stored in animage frame memory 430. If the selected scanning mode utilizes a singletransmit focal point, the grayscale signals are transmitted to the backend ASIC 50 for scan conversion. Prior to leaving the ASIC 40, thegreyscale signals can be frame averaged by an infinite impulse response(IIR) filter 436 which utilizes image frame memory 430 as a frame bufferand incorporates one multiplier and two adders to perform frame to frameaveraging of the form

F _(out)=(1−α)F _(out−1) +αF _(new) =F _(out−1)+α(F _(new) −F _(out−1))

[0031] where the multiplier coefficient is a. If the coefficient is abinary number (e.g., 0.5, 0.25, 0.125) F_(out) can be obtained with anadd-shift-add operation.

[0032] If multiple focal zones are used, each received scanline segmentis stored in the r.f. memory 420 until scanline segments from the entiredisplay depth have been received. Preferably the scanline segments forone complete focal zone are acquired before transmitting and receivingsegments from another focal zone. When all segments for a scanline havebeen acquired, each complete scanline is then read out of the r.f.memory and filtered by the FIR filter 432, which smoothes the boundariesbetween the segments for a more pleasing, artifactfree image.

[0033] If both multiple zone focusing and synthetic aperture are used,the scanline segments of both halves of the aperture are received overthe full focal zone and assembled in the r.f. memory 420. Correspondingscanline segments are then received from other focal zones and joinedwith the segments from the first received focal zone. The completedscanlines are then filtered by FIR filter 432 to smooth the boundariesbetween segments.

[0034] The user may choose to process the grayscale image with certainimage enhancement features, such as depth dependent filtering or specklereduction such as the frequency compounding technique described in U.S.Pat. No. 4,561,019. These optional processing techniques necessitate theuse of the filters 412 and 414 for separate bandpass filtering of thescanline signals and absolute value detection rather than quadraturedetection. In the case of depth dependent filtering the received echosignals are multiplied by cosine functions in both of filters 412 and414, but with coefficients chosen so that one filter produces outputsignals in a high passband and the other produces output signals in alow passband. The output signals produced by the two filters are of theform I₁=h₁(t)cos ω_(H)t and I₂=h₂(t)cos ω_(L)t. These two output signalsare amplified in gain stages 416 and 418 by complementary time varyinggain control functions. The high frequency passband signals 11 areinitially amplified strongly, then the gain is decreased as echo signalsare received from increasing depths along the scanline. In acomplementary manner the low frequency passband signals 12 are initiallyat a low level, then amplified in an increasing manner with depth as thehigh frequency gain is rolled off. Thus, signals at shallow depths willexhibit a relatively high passband, and signals from greater depths willpass through a relatively lower passband which reduces high frequencynoise at the greater depths. Detection in the CORDIC processor ofcircuit 428 is performed by absolute value detection by squaring I₁, andI_(z), then summing the results. Following summation the signals are logcompressed to the desired grayscale mapping characteristic.Alternatively, the signals passed by the separate passbands are summedby the adder 424, then detected by absolute value detection in thedetection and compression circuitry 428 and mapped.

[0035] The same processors can be used to provide speckle reduction byfrequency compounding. The coefficients of one of the filters 412, 414are chosen to filter the received signals by a high frequency passband,and the coefficients of the other filter are chosen to filter thereceived signals by a contiguous low frequency passband. Thecoefficients ofxhe gain stages 416, 418 are chosen to equalize theresponses of the two passbands. The signals of the high and lowpassbands are coupled to the detection and compression circuitry wherethe passbands are separately detected through absolute value detectionas described above, then the detected signals are log compressed to thedesired grayscale mapping characteristic and summed on a spatial basis.

[0036] The processing of Doppler echo signals for power Doppler (CPA)display is shown in FIG. 5 together with the flowchart of FIG. 7. Eachscanline vector is scanned repetitively, for instance eight times, toassemble an ensemble of Doppler information along the vector. Eachreceived scanline of echo signals is normalized by the normalizationcircuit 410 and undergoes decimation band pass filtering in the filter412. Each scanline of the ensemble is stored in the r.f. memory 420until a complete ensemble has been accumulated. The scanlines of eachensemble are coupled by the multiplexer 422 to the four multiplierfilter 414, which performs wall filtering and Doppler power estimationthrough matrix filtering. Wall filtering is performed by selection ofappropriate multiplier coefficients and the matrix filtering is of theform $\begin{bmatrix}Y_{1} \\Y_{2} \\Y_{3} \\. \\. \\. \\Y_{n}\end{bmatrix} = {\left\lbrack {\begin{matrix}a_{11} \\b_{11} \\c_{11} \\. \\. \\. \\z_{11}\end{matrix}\begin{matrix}a_{12} \\b_{12} \\c_{12} \\. \\. \\. \\z_{12}\end{matrix}\begin{matrix}a_{13} \\b_{13} \\c_{13} \\. \\. \\. \\z_{13}\end{matrix}\begin{matrix}\ldots \\\ldots \\\ldots \\\quad \\\quad \\\quad \\\ldots\end{matrix}\begin{matrix}a_{1n} \\b_{1n} \\c_{1n} \\. \\. \\. \\z_{1n}\end{matrix}} \right\rbrack*\begin{bmatrix}x_{1} \\x_{2} \\x_{3} \\. \\. \\. \\x_{n}\end{bmatrix}}$

[0037] where x₁ . . . x_(n) are spatially aligned signals from theensemble of scanlines and Y₁ . . . Y_(n) are output Doppler values. In apreferred embodiment a four multiplier filter is used for matrixfiltering, and the filtering is performed sequentially andincrementally. Intermediate products are accumulated as described above,thereby extending the filter length. For example, in processing theabove matrix with a four multiplier filter, the intermediate productsa₁₁x₁+a₁₂x₂+a₁₃x₃+a₁₄x₄ are formed initially and summed in theaccumulator. Then products a₁₅x₅+a₁₆x₆+a₁₇x₇+a₁₈x₈ are formed by themultipliers and summed in the accumulator with the previously computedintermediate products. By accumulating intermediate products in thismanner the four multipliers and accumulator can be extended to a filterof any desired length, restricted only by the maximum processing timeavailable. The Doppler values are coupled to the detection andcompression circuitry 428 through the gain stage 418 and the multiplexer426, where the Doppler signal amplitude at each echo location along thescanline is detected through absolute value detection of the form$Y = {\sum\limits_{n}^{1 - n}\quad {Yn}^{2}}$

[0038] The Doppler values Y are compressed and scaled using the CORDICprocessor of the detection and compression circuitry 428.

[0039] Once the Doppler signal amplitude values have been detected andfiltered by FIR filter 432, the resulting values are spatially storedand image clutter is removed by a flash suppression processor 434, whicheliminates large frame to frame variations in the displayed signals.Flash suppression processor 434 may operate by any of a number of knownflash suppression techniques, such as frame to frame comparison andelimination or the notch filtering technique of U.S. Pat. No. 5,197,477.A preferred technique for flash suppression processing is min-maxfiltering as described in detail in the parent, U.S. Pat. No. 5,722,412.

[0040] The image frame memory 430 is capable of storing either a grayscale frame or a power Doppler frame. Each frame can be temporallyfiltered by the IIR filter 436, which performs frame averaging on apoint-by-point basis as described above. The temporally filtered imageinformation is then provided to the back end ASIC 50 for scan conversionand display.

[0041] The sequences of operating the digital signal processing ASIC 40for B mode (two dimensional) echo and Doppler processing, respectively,are outlined in the flowcharts of FIGS. 6 and 7, respectively. Thenumber in each flowchart block of FIGS. 6 and 7 refers to the numberedprocessor in the ASIC block diagram of FIG. 5.

[0042] The image frame memory 430 of the digital signal processing ASIC40 shares a common architecture and implementation technology with theframe buffer memory of the back end ASIC 50. To take advantage of thiscommonality and the resultant efficiency in ASIC fabrication anddensity, the image frame memory 430 and its associated flash suppressionprocessor 434 and IIR filter 436 can be located on the back end ASIC 50,thereby partitioning the digital signal processing ASIC and the back,end ASIC at the output of FIR filter 432. Thus, the digital signalprocessing function of FIG. 5 up through the output of FIR filter 432,or all of the functions shown in FIG. 5 can be fabricated on a singleintegrated circuit chip, depending upon this partitioning choice andother integrated circuit layout considerations.

[0043] The back end ASIC 50 is the location of the RISC processor 502,which is used to coordinate the timing of all of the operations of thehandheld ultrasound system. The RISC processor is connected to all othermajor functional areas of the ASICs to coordinate, process timing and toload buffers and registers with the data necessary to perform the typeof processing and display desired by the user. Program data foroperation of the RISC processor is stored in a program memory 52 whichis accessed by the RISC processor. Timing for the RISC processor isprovided by clock signals from the clock generator located on the frontend ASIC 30. The RISC processor also communicates through a PCMCIAand/or infrared transmitter interface, by which the processor can accessadditional program data or transmit image information remotely. Theinterface can connect to a telemetry link or a modem for thetransmission of ultrasound images from the handheld unit to a remotelocation, for instance.

[0044] The RISC processor is operated under user control by commands andentries made by the user on the user control 70. A chart showing controlfunctions, the type of controls, and their description is shown in FIG.8. It will be appreciated that a number of functions, such as patientdata entry, Cineloop operation, and 3D review, will operate through menucontrol to minimize the number of key or button controls on the smallhandheld unit. To further simplify the unit a number of operatingfunctions are preprogrammed to specific diagnostic applications and willoperate automatically when a specific application is selected. Selectionof B mode imaging will automatically invoke frequency compounding anddepth dependent filtering on the digital signal processing ASIC 40, forinstance, while a four multiplier filter will automatically be set up asa wall filter on the DSP ASIC when Doppler operation is selected. Themenu selection of specific clinical applications can automaticallyinvoke specific feature settings such as TGC control characteristics andfocal zones, for example.

What is claimed is:
 1. A method for reducing signal bandwidth in adigital signal processor of a handheld ultrasound device, said methodcomprising: receiving scanline signals in a normalization circuit,wherein said receiving scanline signals is at an input rate; couplingscanline signals to a first finite impulse response filter, wherein saidscanline signals are multiplied by a coefficient and produce a firstaccumulated signal; and coupling said scanline signals to a secondfinite response filter, wherein said scanline signals are multiplied bya coefficient and produce a second accumulated signal, wherein saidfirst and second finite impulse response filters provide said first andsecond accumulated signals at a rate less than the input rate.
 2. Themethod of claim 1, wherein each of said first finite impulse responsefilter and said second finite impulse response filter comprises amultiplier and an accumulator.
 3. The method of claim 1, wherein saidnormalization circuit normalizes said scanline signals for beam andaperture variation.
 4. The method of claim 1, said method furthercomprising: multiplying said scanline signals by a coefficient toproduce normalized scanline signals.
 5. The method of claim 1, whereinsaid scanline signals are coupled by a multiplexer to said second finiteimpulse response filter.
 6. The method of claim 1, wherein saidcoefficients are supplied by a coefficient memory.
 7. The method ofclaim 1, wherein said first finite impulse response filter produces inphase (I) signal samples.
 8. The method of claim 1, wherein said secondfinite impulse response filter produces quadrature (Q) signal samples.9. The method of claim 1, wherein said coefficient associated with saidfirst finite impulse response filter is chosen to multiply said scanlinesignals by a weighted cosine function.
 10. The method of claim 9,wherein said coefficient associated with said second finite impulseresponse filter is chosen to multiply said scanline signals by aweighted sine function.
 11. The method of claim 1, wherein said signalbandwidth is reduced to equal the transducer bandwidth of said handheldultrasound device.
 12. The method of claim 1, wherein said signalbandwidth is reduced to match the display bandwidth of a display monitorof said handheld ultrasound device.
 13. The method of claim 1, whereinthe effective lengths of each of said first and second finite impulseresponse filters are adjusted.
 14. The method of claim 1, wherein saidfirst and second finite impulse response filters are used to reduce r.f.noise.
 15. The method of claim 1, wherein the output rate is decimatedby a variable factor.
 16. A digital signal processor for use in ahandheld ultrasound device comprising: a normalization circuit forreceiving and adjusting scanline signals for beam and aperturevariation; at least two finite impulse response filters for receivingand multiplying scanline signals; a r.f. memory for storing partiallysummed scanlines from a portion of a full aperture acquired following atleast two separate pulse transmissions; and an adder for combining saidpartially summed scanlines to form full aperture scanlines.
 17. Thedigital signal processor of claim 16, wherein said at least two finiteimpulse response filters are coupled to said r.f. memory by amultiplexer.
 18. The digital signal processor of claim 16, furthercomprising: a detection and compression circuit, wherein after said fullaperture scanlines are formed, said full aperture scanlines are coupledfrom said adder to said detection and compression circuit.
 19. Thedigital signal processor of claim 18 wherein said detection andcompression circuit compresses and scales to map said full aperturescanlines to a desired range of display gray levels.
 20. A digitalsignal processor for use in a handheld ultrasound device comprising:means for adjusting scanline signals for beam and aperture variation;means for multiplying normalized scanline signals from said scanlinesignals; and means for forming a synthetic aperture, wherein partiallysummed scanlines from a portion of a full aperture are acquiredfollowing at least two separate pulse transmissions and combined to formfull aperture scanlines.
 21. The digital signal processor of claim 20,wherein said means for forming a synthetic aperture comprises: a r.f.memory for storing said partially summed scanlines when acquiredfollowing said at least two separate pulse transmissions; and an adderfor combining said partially summed scanlines to form said full aperturescanlines.
 22. The digital signal processor of claim 20, furthercomprising: means for compressing and mapping said full aperturescanlines to a desired range of display gray levels.